Alternating-current motor.



No. 759,967. PATENTED MAY 17, 1904.

A. J. GHURGHWARD.

ALTERNATINGCURRENT MOTOR.

APPLICATION nun MAR. 29. 1897.

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WITNESSES 6. Jlkxander-J (xurchrrard,

IZ /%I5Z M HIS ATTORNEY No. 759,967. PATENTED MAY 17, 1904. A. J.GHURGHWARD.

ALTERNATING CURRENT MOTOR.

, APPLICATION FILED MAR. 29. 1897.

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WITNESSES 56. mm

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PATENTED MAY 17, 1904.

A. J. GHURGHWARD. ALTERNATING CURRENT MOTOR.

APPLICATION FILED MAR. 29. 1897.

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UNITED STATES Patented May 17, 1904.

PATENT OFFICE.

ALTERNATING-CURRENT MOTOR.

SPECIFICATION forming part of Letters Patent No. 759,967, dated May 17,1904:.

Application filed March 29, 1897. Serial No. 629,849. (No model.)

To (Ml whmn it may concern.-

Be it known that I, ALEXANDER J. CHURCH- WARD, a citizen of the UnitedStates, and a resident of Brooklyn, in the county of Kings and State ofNew York, have invented a certain new and useful Alternating-CurrentMotor, of which the following is a specification.

My invention relates to single-phase alternating-current motors of thetype in which the winding and general organization is that of anyordinary continuous'or direct current motor or dynamo. As is well known,this class of machines will start and developpower when fed withalternating currents to both field and armature and will accelerate andfinally reach a speed which is synchronous with the alternations; butthe machine is not self-regulating and will run away under light load.nating-current motors are ordinarily very inefiicient, among otherthings, because of the losses arising from self-induction of their partsunder the action of the alternating currents-a source of loss, however,which may be largely avoided if the machine may be kept running at aspeed synchronous with the rate of alternations, provided that 'it is soconstructed as to primarily have a low self-induction. The losses fromself-induction are also largely augmented, owing to the fact that suchmotors in order that they may have a large starting torque have beenhitherto so constructed that of necessity they have also a highself-induction, which remains as a source of loss even after the motoris brought up to whatever working speed is chosen for it.

The general object of my invention is to permit machines of this classto be operated with high efficiency by alternating currents passed tothe direct-current armature-winding through the direct-currentcommutator; and to this end the invention consists, broadly, in

the combination, with said machine, of means 7 for keeping the armatureat synchronous or similar predetermined speed while so operated.

My invention consists also in the combination, with analternating-current motor, of auxiliary means whereby an extra voltagemay be produced to overcome the high selfinduction of the motor atstarting.

Such machines, moreover, run as alter My invention consists also in thespecial combinations of apparatus, as hereinafter more particularlydescribed and claimed.

" The invention is particularly useful in connection with series-Woundmotors having a continuous current armature winding and commutator. Whena motor of this kind is run in synchronism with the generator, thearmature or revolving part becomes in reality a constant field excitedby a direct currentthat is, by the alternating current rectified by thecontinuous-current commutator, to which the armature-coils are connectedand to which the alternating currents are fed. This will be readilyappreciated when it is considered that the current generated by thedirect-current armature is primarily an alternating current which isrectified by means of the commutator. Conversely, if an alternatingcurrent is supplied to said armature through the medium of itscommutator the result will be, if the armature is in step with thealternations, that the current as it flows in the armature will be adirect current, and the armature will exhibit a field with constantpoles. The poles of the field-magnet will, however, alternate and willact magnetically as a revolving field to rotate the armature. Operatedunder this condition there is no loss by hysteresis in the rotor,because there are no reversals of magnetism taking place and the currentbeing continuous there is no self-induction in the wires; but topreserve this condition some regulating means must be provided forholding the motor in or about synchronism. This may be secured byvarious meansas, for instance, by any suitable regulating device adaptedto regulate the alternating current fed to the machine, so as todiminish the current when the speed rises above the synchronous orpredetermined speed and to increase it when the speed falls below suchspeed. This may be accomplished in various ways, as by resistanceinterposed in and withdrawn from the circuit, by varying the impressedelectromotive force through cutting in and out the coils of atransformer or autoconverter, or in other ways regulating the voltage.The regulation might also be effected in various other ways by cuttingfield-coils of the machine in and out of clrcuit to vary the strength ofthe field. The regulation may be controlled either by hand orautomatically by a suitable centrifugal governor or other deviceresponsive to changes of speed. 1t has been shown that if the motor runsin synchronism there will be no more loss due to eddycurrents,hysteresis, or self-induction in the rotor than in the field of adirect-current motor. If we desire to run the motor at a slower speed,the loss in the rotor will be increased. 1f, however, we run it athalf-speed, the losses will only be due to half the number of reversalsof the line. For example, synchronous speed, eighteen hundredrevolutions per minute, four poles, equals seven thousand two hundredalternations; half speed, nine hund red revolutions per minute, fourpoles, equals three thousand six hundred alternations. So, also, of anyother speed which is a submultiple of the synchronous speed, so that byrunning at such predetermined speeds we can vary the speed within alarge range without much loss in efficiency.

1n the accompanying drawings, Figure 1 is an end elevation of a motorand automatic attaclnnent suitable for carrying out my invention. Fig. 2is a plan view. Fig. 3 is a side elevation of the field-magnet of themotor; Fig. at, a detail of a form of centrifugal governor. Figs. 5, 6,7, 8, and 9 are diagrams showing the circuits of the apparatus in someof its modifications. Figs. 10 and 11 show a further modification.

In the drawings 1 have shown the invention as carried out in connectionwith a fourpole machine, the armature A of which is wound like anydirect or continuous current generator or motor and is provided with theusual commutator, the cylinder of which is indicated at a and thebrushes at I), disposed about said cylinder in the usual manner. Thefour-field magnet-poles are shown at c and the field-magnet coils at C.By suitable connections the field-coils are in series with the armature,as indicated in the diagram, or are otherwise connected to thesupply-circuits, so that alternating currents will flow to said coils instep with or at the same frequency with the alternating currents fed tothe commutator-brushes and through the commutator-cylinder to thearmature.

By preference I organize and operate the motor as a series motorthat is,with the armature and field coils in series with one another and this isthe condition of the machine both during starting or acceleration andwhen running at normal speed. The machine is fed with alternatingcurrents from any desired source-as, for instance, from the secondary ofa transformer or converter 1), as indicated in the diagrams, the primaryof which is supplied from mains or supply-wires L L. In Figs. 5 and 6the transformer supplies the motor directly, and in Figs. 7 and 8 thecurrent from the secondary is modified by an autotransformer I). r

In Figs. 5 and 6 the means shown for regulating the speed of the motorconsists of a sectional secondary (Z for the transformer and a suitableswitch F, moving over a set of contacts, (munbered 1 2 3 4,) to whichthe sections of coil (Z are connected, as shown. The secondary feedsalternating currents through the switch, the armature, and the field (,3in series, and the switch by its movement increases or diminishes thenumber of coils (l in action. hen the speed falls from the desiredsynchronous or other predetermined speed, the switch is turned toincrease the number of coils (l in action, and thus increase the i1n1)ressed electromotive force, and when the speed rises above thepredetermined or synchronous speed the switch is turned in the oppositedirection to decrease the number of coils It and lower the impressedelectromotive force. \Vhen the machine is running at less than the fullsynchronous speed or in the starting operation, the alternating currentflows as an alternating current in both armature and field in serieswith one another; but when the synchronous speed is reached the currentflows as a continuous or direct current in said armature and as analternating current in the field, but said field and armature are inseries,as before. By suitable adjustment of the switches, the armaturemay be kept at the synchronous speed. If desired, the machine may bekept at a lower than synchronous speed in the same manner e as, forinstance, at half speed or quarter speed-by proper adjustment of theregulating devices and will then work at high elliciency.

The switch or other regulator may be operated by hand or automaticallyby any device responsive to differences of speed as, for instance, by acentrifugal governor, (typified at Gr, Figs. 5 and 6,) that may beconnected with the switch or other device in any suitable way. Asuitable construction of governor and switch is shown in Figs. 1, 2, and4 and will be presently described.

The operation of the devices so far as de scribed would be as follows:At starting or at low speed the switch would be on contact 1. The motorwould then be supplied with all of the voltage due to all the coils dbetween con tact 1 and the opposite end of coils //,connect ed to thefield C. The high self-induction of the motor at starting would becompensated for by the large voltage thus supplied. As the motorincreases in speed, the switch would be turned, decreasing the voltageof the applied current until the synchronous speed is reached, at whichtime the switch rests on a contact such that the voltage would keep themotor running at that speed. On further increase of speed the switchwould further decrease the voltage, and the motor will drop back to thesynchronous or other predetermined speed.

The sectional transformer switch and motor combined and operated asshown in Figs. 5

and 6 are not specifically claimed herein, as they form the subject ofclaims in another application for patent, filed by me March 29, 1897,Serial No. 629,852.

When the motor is at rest and current is turned on, there areeddy-current losses, selfinduction, and losses due to hysteresis, whichall tend to reduce the useful voltage of the line by increasing theself-induction of the motor, so that if the motor has to have a largestarting torque the self-induction will be too great to pass sufficientcurrent to give the necessary torque. To allow an excess of current toflow when starting the motor, I provide some auxiliary means inconnection therewith for permitting or furnishing such excess current,and thereby avoid the necessity hitherto existing of using a motor whichin order to get the desired starting torque has been made unnecessarilylarge or has been so constructed that when running at speed it will beinefficient. Such auxiliary means may be extra turns in the converter orin the autotransformer, so that if the machine is wound to run on, say,one hundred volts we can momentarilyget two hundred volts. Thecentrifugal governor or other suitable means may be used to cut out suchextra turns. These extra turns are shown as connected to an auxiliarycontact X either directly or through a hand-switch S. The same effectcould be produced by reducing the self-induction of the motor atstarting by placing the brushes in relation to the field as indicated inthe diagram Fig. 10, when the motor is at rest. This position will givethe least self-induction, and therefore allow more current to pass atstarting. As the motor gains speed the brushes are shifted to positionshown in diagram Fig. 11, the position for full load, when theself-induction will be greatest, but the running efficiency will behighest. By these means the greatest starting torque and the highestrunning efficiency can be obtained. This method of operatingsingle-phase alternating-current motors I do not claim herein, as itforms the subject of claims in another application for patent, filed byme March 29, 1897, Serial No. 629,853.

In Figs. 7 and 8 the sectional autotransformer D is used in connectionwith the switch as a regulator. 'The coil is interposed as shown in' thecircuit between the source D of alternating currents and the motor andswitch, and the coil-sections of the autotransformer are connected tothe switch, so that at speed again.

supplied thereto from the smaller number of sections of saidautotransformer remaining in shunt to the motor. Auxiliary sections onsaid transformer controlled by switch S may be used for startingpurposes, as already stated.

Fig. 9 shows how by putting additional sectional windings on thefield-magnet C and cutting the same in and out by means of the governoror other actuating or controlling device the strength of the field maybe varied to keep the motor at the required synchronous speed, thenumber of coils being diminished should the speed increase, and therebycutting down the strength of the field, and being at their maximum togive the maximum field at the start. The source from which the motor issupplied is supposed in this case to be adapted to give an alternatingcurrent of constant strength. The sectional winding is so proportionedthat after the synchronous speed is attained further adjustment of theregulator on further increase of speed will so decrease the strength offield as to bring the motor back to synchronous speed, and a fall belowsynchronous speed will increase the strength of field and bring themotor up to ating single-phase self-starting alternating motors, such asdescribed, I do not claim herein, as it forms the subject of claims inanother application, filed by me March 29, 1897, Serial No. 629,851.

A suitable mechanical construction of'centrifugal governor and apreferred construction of controlling-switch are illustrated more indetail in the Figs. 1, 2, and 4:. The governor-balls consist of theelbow-levers l, mounted in abracket N, connected to the motor-shaft. Theoutward radial movement of the balls is resisted by a spring connectingthem. The levers engage in a groove in a sleeve 0, movable axially onthe shaft and act- This special method of opering against a lever P,which is connected to a rod Q, carrying the switch-contact, composed inthiscase of a pair of springs R R, attached to the rod and in electricalunion with one another. This contact slides in the space between theseries of contact-blocks t t, insulated from one another in a suitablebox or holder, and a continuous plate or block t, mounted in a box atthe opposite side of the track of the contact R R. The sections of coilor circuits to be controlled are connected to the contacts 2, t and theopposite pole of the circuit to t, and the contact R R of the switchthus formed will in obvious manner as it moves to and fro under theaction of the governor cut the coil-sections into and out of circuit. Aretractorspring W acts on the switchbar Q to help reverse its movementwhen the speed falls. To obviate sparking as the switchcontact ridesover the series of contacts, it should under ordinary conditions of usemomentarily brldge successive contacts-that 1s,

make contact with a succeeding before leaving a previous contact. Thismeans a momentary short-circuiting of adjoining contacts, whichintroduces a serious difliculty when the set of coils connected to theseries of contacts carries an alternating current. This diflicultyarises from the fact that the section of coil short-circuited will bearthe relation to others in circuit at the time of a secondary of atransformer, and heavy currents will be generated in it, which if longcontinued will damage the switch-contacts and will give rise to adamaging are at the instant of break of contact. To obviate thisdiiiiculty, 1 provide means. for giving the switch a snap action as itpasses from each contact of the series to another in both directions ofadjustment. This snap action may be provided by a bar K, having a seriesof projections or teeth and intermediate spaces, over which rides aspring actuated catch or detent in the form, preferably, of afriction-roller It, carried by a spring attached to the switch-rod Q. Atin the rod Q or any other suitable 'point in the connections there isinterposed a lost motion by means of a pin-and-slot connection, asindicated, to per mit the switch to move freely under the operation ofthe spring-actuated catch or detent as the latterslips into eachintermediate space between projections on bar K in obvious manner afterhaving been forced over the summit of one of said projections. The partsare properly arranged so that this quick or snap action will cause thecontact to snap from each contact-point to the next.

As will be obvious, the form of bar K and detent 7L, aswell as the formand manner of application of the spring which forces the detent into thedepressions, and thereby causes the longitudinal movement of theswitch-bar Q, may be largely varied. 1t is also obvious that either thebar K or the detent might be attached to the rod Q and the other befixed in position on a suitable support.

WV hat 1 claim as my invention is- 1. A single-phase alternating-currentmotor having an armature provided with a continuous-current winding andcommutator and operated by alternating current passed to itsarmature-coils through said commutator, in combination with an automaticregulator responsive to changes in the speed of the armature while sooperated, and adjusted as described to keep the armature at asynchronous speed.

2. A single-phase alternating-current motor having any suitabledirect-current armature-winding and commutator, as described, to adaptthe machine for self-starting, combined with a regulator responsive tovariations in speed of said motor and adjusted, as described, to keepthe armature running at a speed synchronous with the alternations, asand for the purpose described.

3. The combination with a self-starting single-phase alternating-currentmotor having a continuous or direct current armature-winding fed withalternating current from any desired source, of auxiliary means adaptedto cause an excess of current to flow when starting, as and for thepurpose described.

4:. The combination with a series-wound motor having an armatureprovided with a direct-current winding and commutator, and operated byalternating currents fed from any desired source, of an autotransformerhaving a sectional winding, and means for automatically increasing thelength of winding in series with the motor and diminishing the length ofwinding in shunt thereto as the speed increases, as and for the purposedescribed.

The combination with a self-starting alternating current motor, of anautotransformer having a sectional winding, a switch for saidtransformer, and means for automatically controlling said switch by theoperation of the motor so as to maintain the same at constant speed, asand for the purpose described.

6. Aself-starting single-phase alternatingcurrcnt motor consisting of amachine having any suitable direct or continuous current winding incombination with auxiliary means for modifying the induction of thecircuit to give a larger current flow at starting.

7. The combination with a centrifugal governor, of a switch having aseries of contacts and connected therewith through devices permitting alost motion, and means for giving said switch a snap or quick action asit passes from each contact of the series to the next, forward andbackward.

8. The combination as a means for automatically controlling analternating-current motor of a sectional coil carrying an alternatingcurrent, a series of contacts to which said sections are connected, acontact adapted to reciprocate over the same and to preserve connectionin passing from one to the other, and means for giving to said contact asnap or quick action at the instant it short-circuits one of thecoil-sections.

9. The combination as a means for automatically controlling analternatingcurrent motor of a reciprocating switch-contact and a seriesof contacts over which the same moves, a bar having a series ofprojections or teeth, a detent adapted to slip into the depressionsbetween the same, an actuating-spring, and means for providing a lostmotion in the actuating connections of the switch, as and for thepurpose described.

Signed at New York, in the county of New York and State of New York,this 20th day of February, A. 1). 1897.

ALEXANDER J. (lllUltCllWMtl). lVitnesses:

WM. H. (JArnL, D. H. Deexnn.

ITO

